The present invention relates to a glass; and more particularly to a glass doped with rare earth ions for use in an optical amplifier.
A silicate glass based on a quartz glass is dominantly used as a host glass of a gain medium fiber in optical amplifiers for optical communication. It has excellent properties on facilities of fiber fabrication, chemical stability and optical transparency. However, the fluorescence of silicate glass suffers from its high phonon energy in many cases. The transition with energy gap less than 4,500 cmxe2x88x921 is not capable of effectively performing laser oscillation or optical amplification in the silicate glass.
In order to overcome the above problems, a special glass, e.g., a fluoride or a chalcogenide glass, having low phonon energy has been proposed. However, the special glass still has some problems such as thermal stability, chemical durability, resistance to humidity.
Recently, there has been considerable attention paid to a tellurite glass which has phonon energy (600xcx9c800 cmxe2x88x921) higher than those of the fluoride (400xcx9c500 cmxe2x88x921) and the chalcogenide (300xcx9c400 cmxe2x88x921) glasses, but lower than that of the silicate glass (1,100 cmxe2x88x921). Therefore, the tellurite glass can suppress non-radiative transition through multi-phonon relaxation in the transition with energy gap of 3,500 cmxe2x88x921 or more. The tellurite glass has larger absorption and emission cross-sections than those of the silicate glass and the fluoride glass, thereby obtaining relatively strong fluorescence. Further, the tellurite glass has higher thermal stability, chemical durability and resistance to humidity than those of the fluoride and the chalcogenide glasses, thereby being expected to have relatively higher reliability when used in optical communication system.
U.S. Pat. No. 5,251,062 discloses a tellurite glass with a composition of: 58xcx9c84 mole % of TeO2, 0xcx9c24 mole % of Na2O and 10xcx9c30 mole % of ZnO. The tellurite glass may be applicable to an optical amplifier or a solid laser oscillator utilizing an optical fiber or other optical waveguide structures. The tellurite glass has several advantages as follows: it easily give a different refractive index to a core and a cladding; and to draw a preform made of the tellurite glass into an optical fiber with ease, while TeO2xe2x80x94ZnOxe2x80x94Li2O glasses proposed in the prior patent document (U.S. Pat. No. 3,836,871) are of compositions inapplicable to the optical fiber. U.S. Pat. No. 5,798,306 discloses rare-earth ion doped oxyhalide glass for laser, which comprises the substitution of fluorine for oxygen in the glass having a representative composition of 50 mole % of SiO2, 25 mole % of CaO and 25 mole % of Al2O3. When Er2O3 can be doped with amounts of 0.01 mole % to 1.2 mole % (500 ppm xcx9c5.68% by weight) into this glass. There is not concentration quenching in fluorescence. The fluorescence lifetime is longer in the fluorine-substituted glass than that of the pure oxide glass when same amounts of Er2O3 are doped into both glasses.
U.S. Pat. No. 4,652,536 discloses glasses, which comprise 60xcx9c85 mole % of TeO2, 0xcx9c25 mole % of Li2O, 0xcx9c35 mole % of Na2O, 0xcx9c25 mole % of K2O, 0xcx9c25 mole % of Rb2O, 0xcx9c15 mole % of Cs2O, 0xcx9c10 mole % of MgO, 0xcx9c5 mole % of CaO, 0xcx9c5 mole % of SrO, 1xcx9c30 mole % of BaO, 0xcx9c30 mole % of ZnO, 0xcx9c30 mole % of PbO, and 0xcx9c5 mole % of La2O3+ZrO2+TiO2+Nb2O5+Ta2O5+WO3, wherein the amount of K2O+Rb2O+Cs2O is limited to 1xcx9c25 mole %, and the amount of ZnO+PbO is limited to 1xcx9c30 mole %. These glasses have lower light path difference with temperature change and enhanced figure of merit for acoustic optical devices than those of the prior glasses. These glasses may be used in acoustic optical devices such as light modulator and light path conversion devices, and can be also used as a glass with high refractive index or a glass with low melting point.
There have been other research results for tellurite glasses (See, J. S. Wang, E. M. Vogel and E. Snitzer, xe2x80x9cTellurite Glass: A New Candidate for Fiber Devicesxe2x80x9d, Optical materials, 3, 187-203(1994), D. L. Sidebottom, M. A. Hruschka, B. G. Potter and R. K. Brow, xe2x80x9cStructure and Optical Properties of Rare-Earth-Doped Zinc Oxyhalide Glassesxe2x80x9d, J. of Non-cryst. Solids, 222, 282-289(1997), Zhengda pan and Steven H. Morgan, xe2x80x9cRaman Spectra and Thermal Analysis of A New Lead-Tellurium-Germanate Glass Systemxe2x80x9d J. of Non-Cryst. Solids, 210, 130-135(1997)).
However, the tellurite glass still has a problem of being easily crystallized when heated up to a crystallization temperature, that is, between the glass transition temperature and the melting temperature. This problem may result in cutting off the optical fiber during the fiber drawing process. It may also largely increase an optical loss due to fine crystals within the optical fiber.
Therefore, there would be needed to solve the above-mentioned problem in the crystallization of the tellurite glass and to provide the tellurite glass with enhanced optical properties for light waveguide type optical amplifiers.
It is an object of the present invention to provide a glass composition applicable to a gain medium glass for rare-earth ions doped light waveguide type amplifiers.
It is also another object of the present invention to provide a tellurite glass, which is hardly crystallized or phase-separated during the fabrication of an optical fiber, thereby being stable thermally and chemically.
In accordance with one aspect of the present invention, there are provided a glass material suitable for a waveguide of an optical amplifier, comprising: 20xcx9c70 mole % of TeO2; 1xcx9c30 mole % of In2O3 or a combination of GeO2 and In2O3 oxide; 0.001xcx9c10 mole % of a rare earth ion dopant; 5xcx9c30 mole % of MO, M being a material selected from a group consisting of Mg, Ca, Sr, Ba, Zn and Pb; and optionally 1xcx9c20 mole % of R2O , R being a material selected from a group consisting of Li, Na, K, Rb and Cs.
In accordance with another aspect of the present invention, there are provided a glass material suitable for optical waveguide type amplifier, comprising: 20xcx9c70 mole % of TeO2; a heavy metal oxide; 0.001xcx9c10 mole % of a rare earth ion dopant; 5xcx9c30 mole % of MO, M being a material selected from a group consisting of Mg, Ca, Sr, Ba, Zn and Pb; optionally 1xcx9c20 mole % of R2O, R being a material selected from a group consisting of Li, Na, K, Rb and Cs; and 3xcx9c18 mole % of the metal oxide of MO or/and R2O is substituted by metal halide(s).